The present invention relates to apparatus and methods for measuring an overall flow rate of a fluid with particular emphasis on methods made by combining a plurality of local measurements.
Combining a plurality of local flow measurements made at more than one location in the cross section of a flow profile to generate a composite flow value representative of the overall flow rate can improve the accuracy of the overall measurement. In addition, using multiple flow rate sensors provides a degree of redundancy so that if one local sensor fails, the remaining flow rate sensor or sensors may still be able to provide a usable flow rate indication until repairs are made.
Generating a composite flow output from a plurality of local sensors can be important when measuring a highly inhomogeneous flow. Such a situation can arise, for example, where the flow measurement must be made very close to a piping structure, such as a ninety degree elbow, that can induce swirl or distort the flow profile from what would be expected in a long, straight run of pipe. In cases such as this, dropping the output from a failed sensor and using the outputs from the remaining ones can lead to an unacceptably high error in the measurement. One thing that is needed, but not provided by the prior art, is apparatus and method for generating an acceptably accurate composite flow measurement from a plurality of local sensors when one or more of the sensors is defective.